endpoint to get transactions concerning account from chain

[thepiwo]

• GET /tx/:account: endpoint returning all transactions concerning account
  tx can be fetched from chainstate, find block, filter transactions
• GET /tx/:account:?include_proof=true include merkle proof and block_hash in result, to get the proof fetch the block by hash, build the tx merkle tree, filter the transaction by hash and create the proof via https://github.com/aeternity/gb_merkle_trees/blob/dev/src/gb_merkle_trees.erl#L128

[thepiwo]

this needs the transactions added in #91

[thepiwo]

@HristianHristov @gspasov whats the state of this task?

[gspasov]

@thepiwo The second part of the issue was on hold for us. We wanted to fix the #118 first. Now we'll continue with the second point of this issue.